Hale bopp
HOW SCIENTISTS ARE STUDYING IT
As the orbit of Comet Hale-Bopp brings it
closer to the Sun in late March, scientists will study or will have studied the large and
bright comet using sounding rockets, spacecraft and ground-based observations. Below is a
short description of what Goddard Space Flight Center scientists are doing:
Polar Spacecraft - NASA's Polar spacecraft
will use three of its 11 instruments to study the Comet Hale-Bopp from March 25 to April 2
as the comet nears the Sun. Observation periods occur at 18-hour intervals when the
spacecraft is near apogee (farthest point from the Earth), with two of the periods
extending over three hours. The Polar instruments, the Ultraviolet Imager (UVI) and
Visible Imaging System (VIS), will study the ultraviolet emissions from the comet and will
VIS also will image the comet at selected wavelengths in the visible light. The Polar
Ionospheric X-Ray Imaging Experiment (PIXIE) will look for X-rays in Hale-Bopp. However,
it is not known whether the comet will be shining in the X-ray wavelengths detected by
this experiment, which are much shorter and high-energy rays than those previously
detected in comets.
The Polar spacecraft, launched in February 1996, is currently located
in a polar orbit 32,000 mile (apogee) by 3,200 mile (perigee) from the Earth. Polar is
part of NASA's International Solar-Terrestrial Physics program which includes the Solar
and Heliospheric Observatory and Wind spacecraft.
Sounding Rockets - University scientists
also will use NASA sounding rockets to gather data about Comet Hale-Bopp. NASA Goddard's
Wallops Flight Facility (WFF), Wallops Island, Va., will conduct four sounding rocket
launches starting March 24 through April 5. The missions will be launched for NASA by the
U.
S. Navy at the White Sands Missile Range, N.M. The experiments, which will be launched
shortly after sunset, are being provided by the University of Colorado, Boulder;
University of Wisconsin, Madison; Southwest Research Institute, San Antonio; and Johns
Hopkins University, Baltimore. The payloads, launched on two-stage Black-Brant IX rockets
to altitudes of 175 to 240 miles, will observe the comet in the ultraviolet wavelengths of
light for about five minutes before returning to Earth. The payloads will be recovered
following a parachute descent at White Sands.
International Ultraviolet Explorer (IUE) -
First observations of Comet Hale-Bopp from space were conducted with International Extreme
Ultraviolet Explorer in September 1995. An extensive campaign of synoptic observations of
Hale-Bopp were carried out between May and August 1996. Observations of hydroxyl molecules
(chemical formula, OH) showed that the water production rate from Hale-Bopp far surpassed
any other comet observed at this distance from the Sun. IUE observations ceased in
September 1996 when the IUE observatory was turned off after 19 years of operation.
Ground Observations - Dr. Michael J.
Mumma
of Goddard and his science team used the NASA Infrared Telescope Facility, on Mauna Kea,
Hawaii, to make five observing runs of the comet in 1996 and 1997. (A sixth run is
scheduled for April 1997.) The scientists are studying the composition of the icy nucleus
with infrared spectroscopy. Mumma reports that the team has detected many chemicals which
provide insights into the origin of the cometary material. The saturated hydrocarbons,
methane and ethane, carbon monoxide, hydrogen cyande, (Methyl) alcohol and water found in
the comet are of particular importance. A search for deuterated (heavy) water was
conducted to determine whether the Earth's oceans could have been created by comets.
Additionally, Goddard scientists will be using the Kitt Peak National Observatory's new
Phoenix infrared spectrometer and the 2.1 meter telescope in March-April 1997 to search
for isotopes, isomers, and trace chemicals. Deployment of a new Goddard infrared
spectrometer to the NASA 60-inch telescope on Mt. Lemmon, Ariz. in May is planned and will
be used for high resolution spectroscopy and imaging of Hale-Bopp.
Extreme Ultraviolet Explorer (EUVE) -
Goddard scientists using the EUVE spacecraft detected X-rays in Hale-Bopp in mid-September
1996, and have requested follow-up observations this summer.
The scientists searched for
soft X-ray emission from Comet Hale-Bopp, to further understand X-ray emission mechanisms
in comets. Both images and spectra were acquired. The scientists hope to distinguish
between two different models for excitation of X-rays: in the first model, X-rays are
produced when higly ionized atoms in the solar wind impact the cometary coma and are
converted to the next lower charge state consequently emitting an X-ray. In the second
mechanism, solar X-rays are scattered from a population of heretofore unseen tiny dust
grains each containing only a few tens of thousands of atoms. Another key objective is to
determine the abundance of noble gases, neon and helium, in the comet.
These can be used as thermometers to test
the temperature at which pre-cometary ices formed and to constrain the maximum
temperatures to which they were later exposed.
Solar and Heliospheric Observatory (SOHO)
-The Solar Wind Anisotropy (SWAN) on board the SOHO spacecraft, a joint project of the
European Space Agency and NASA, has been recording the large hydrogen could that surrounds
Comet Hale-Bopp for months. This cloud is invisible to the human eye, but is detected by
its glow in the Lyman-Alpha line of hydrogen, an emission in the ultraviolet region of the
spectrum.
Hubble Space Telescope - NASA's Hubble
Space Telescope made a series of observations of Comet Hale-Bopp, particularly the
nucleus, since September 1995. The last observation was made on Oct. 18, 1996. Hubble can
not observe the comet during the next few months because the comet is too close to the Sun
and Hubble's sensitive detectors could be damaged if pointed in that direction.
The next
possible opportunity will be in August 1997. Scientists are currently studying their
research data.
Comet Hale-Bopp NASA Web Sites
Check the following NASA sources for the
latest information on Hale-Bopp:
GSFC - https://www.gsfc.nasa.gov/
NASA HQ - https://comet.
hq.nasa.gov/
WFF -
https://www.wff.nasa.gov/~webcomet.
html
HST -
https://oposite.stsci.edu/pubinfo/PR/95/41.html
JPL - https://galileo.ivv.nasa.
gov/comet/
https://encke.jpl.nasa.gov/index.html
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